The invention relates to a method and device for perforating a mantle of a cylinder in a paper machine, in particular the mantle of a drying cylinder used in a drying group of the paper machine.
At the present time, conventional non-perforated cylinders in a drying group can be converted to so-called UNO-Vac vacuum or suction cylinders by perforating the cylinder mantle. However, when working on drying cylinders in the drying group of a paper machine, the drying cylinders are removed from their place in the machine and then carried aside away from the machine for machining and perforating if desired.
In Finnish Patent Application No. FI 901367, corresponding to U.S. Pat. No. 5,090,846, assigned to the assignee of the instant application, a method and device are described whereby the perforation of a cylinder mantle is carried out on-site at the paper mill where the paper machine is located without detaching the cylinder from the paper machine. Furthermore, in this reference a device is described in which a drilling machine for perforating the cylinder mantle moves on support of separate guides in the axial direction of the cylinder. During the machining and perforating process, the drilling unit is supported both on a mantle face of the cylinder that is being machined, and on a mantle face of an adjacent cylinder.
In FI 901367, the device comprises a spindle box in a multi-spindle drilling machine. Each spindle box contains a unit, e.g. a motor, for rotating drill bits and related power transmission means for simultaneous rotation of all of the drill bits in the drilling machine. The drill bits are placed side by side in the drilling machine. The device further comprises a cylinder, by whose means the jig of the drill bits, i.e. a drill guide, is brought into contact with the face of the cylinder being machined. As the device is supported both on the cylinder being machined and on another adjacent cylinder, which constitutes a support base for the drill guides, a unified, robust structure is formed which permits undisturbed, precise drilling during the machining of the cylinder.
Furthermore, in FI 901367, the spindle box is displaceable relative to the main frame of the drilling machine. A second motor is located in the spindle box and is arranged to displace the spindle box and the drills located therein whereas the first motor is located in the spindle box and is arranged to rotate the drill bits. The drill bits are placed in a fixed position in relation to one another. Therefore, the spacing of grooves in the cylinder being machined must also be fixed because it is preferable that the perforations of the cylinder mantle are placed in the bottom of the grooves.
However, since the spacing of the grooves may vary from cylinder to cylinder, the fixed position of the drill bits will adversely affect the alignment of the drill bits with the grooves so that the perforations may not be drilled into the grooves. This results in an unfavorable arrangement caused by the inflexibility of the drill bits within the drilling machine.